I am trying to network boot Raspberry Pi from my desktop PC with Gentoo Linux.I followed the instructions from Raspberry Pi, with relevant changes for my Gentoo installation.Below are the steps I followed.

I have burned the latest image of Raspbian and booted the Raspberry PI.I ran the update and upgrade using below command

sudo apt-get update && sudo apt-get upgrade

Enabled the USB boot mode using below command

echo program_usb_boot_mode=1 | sudo tee -a /boot/config.txt

Rebooted and verified the boot flag

sudo reboot

After reboot

$ vcgencmd otp_dump | grep 17:
17:3020000a

4. I removed the line that was added in step 2 above and powered off the raspberry pi, sudo poweroff

Removed the sd card and inserted it into PC and copied the root file system